Abstract: In some instances, the application provides methods of culturing host cells comprising a gene encoding a recombinant N protein in a cell culture medium, wherein the cell culture medium comprises: (i) iron at a concentration of less than 1200 ?M; and (ii) citrate at a concentration of less than 2400 ?M. In some instances, the methods comprise culturing host cells expressing a recombinant protein in a cell culture medium at a first temperature; and decreasing the first temperature to a second temperature. In some instances, the methods comprise purifying the recombinant protein by a carbon depth filtration.